Present day manufacturing requirements often necessitate the formation of various workpiece components by welding together two or more metal sheet blanks. Typically, individual sheet blanks are joined by conventional seam or butt welding equipment, such as high energy CO.sub.2 lasers, or electric beam/plasma arc-welding devices. To obtain an effective and complete weld, it is necessary to ensure that the proximal edges of the sheets to be joined are positioned and maintained in a directly abutting orientation during the welding operation.
Where CO.sub.2 lasers are used to perform welding operations, to ensure the formation of a complete weld seam, it is necessary that the edges of the sheet blanks be pre-finished and have a mirror-smooth finish.
Conventional welding apparatus used to join sheet blanks incorporate mechanical clamps for holding the sheets together. The use of mechanical clamps to secure the sheet blanks during welding, however, leads to inefficiencies in workpiece production. In particular, mechanical clamping mechanisms require increased time to clamp and unclamp the sheet blanks in position prior to and after welding. A further disadvantage of conventional apparatus is that the increased clamping time resulting from the use of mechanical clamps inhibits adjustment in the positioning of the proximal edges of the sheets which are to be welded together once the clamps are engaged.
Mechanical clamps which are used in conventional welding apparatus are typically pneumatically or hydraulically operated, requiring that the welding apparatus include large rigid and expensive clamp supporting frames to absorb the clamping forces.
In one attempt to overcome the disadvantages of prior art welding apparatus, magnetic clamping devices have been proposed, as for example, is disclosed in U.S. Pat. No. 5,023,427 which issued Jun. 11, 1991 to Neiheisel et al. The Neiheisel patent discloses an apparatus for aligning steel sheets which are to be welded together by a laser. In the apparatus of Neiheisel, an electromagnet is used to support the sheets in such a manner as to induce opposite magnetic polarities in the proximal edges of adjacent sheets, drawing the sheets together by creating a magnetic attraction therebetween.
While the apparatus of Neiheisel may be useful in aligning proximal edge portions of iron or other ferromagnetic sheets which are of a thickness sufficient to minimize magnetic reluctance therebetween, the apparatus of Neiheisel is poorly suited for use in aligning thinner steel sheet blanks, or sheet blanks which are plated or coated or which are made from non-ferromagnetic materials such as copper, aluminum, plastic and the like.